I printed in PLA which is not very durable for such a small item unless you anneal in an oven afterward. You may have better luck with ABS or PETG.
If the part does not fit tightly around the pen, try scaling down to 99%
When I printed with the long flat part down, the circular part was too weak and the clip part sheered between layers. For this reason, printing with the circular portion down is probably better although this makes the clip portion weaker.
Printing with both x and y axis rotated 30 or 45 degrees and using supports and a raft may result in a more durable print, but you may have blemishes on the print (thanks to The_boots for the suggestion)
With such a small object, bed adhesion and layer cooling time may be an issue. Recommend printing two clips at the same time separated by a few inches if you have problems.
Remember to come back and post what you've printed as Make.
It's good for the designer and the community (that means you)!
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